Japanese Laid-Open Patent Publication No. 2009-135140 (patent document 1) describes a semiconductor device having, for example, a thin-film BOX (Buried Oxide)-SOI structure and capable of achieving the high-speed operation of a logic circuit as well as the stable operation of a memory circuit. According to this semiconductor device, at least three or more well regions different in conductive property are formed in a semiconductor substrate. Through the well regions, a semiconductor substrate region below the first gate electrode of a first field-effect transistor making up the logic circuit is electrically isolated from a semiconductor substrate region below the second gate electrode of a second field-effect transistor making up the memory circuit.